An experimental investigation was carried out on the flapping motion of a turbulent reattaching shear layer downstream of a two-dimensional backward-facing step. The Reynolds number was 2.0 × 104, based on the free-stream velocity and the step height. The aim of this study is to analyze the flapping motion, which is featured unsteadiness of the reattaching shear layer, and its interaction with the recirculation region. High-resolution planar particle image velocimetry was used to measure the separated and reattaching shear layer in a horizontal-vertical plane. The velocity vector fields have shown the reattaching shear layer considerably flaps upwards and downwards as much in scale as approximately one step height from the middle part of recirculation region to the reattachment area. As a result, the recirculation region varies in size and the reattachment point shifts upstream and downstream. By applying singular value decomposition and proper orthogonal decomposition, the flapping motion is decomposed into multiple spatial modes, each of which represents interactions between the reattaching shear layer and recirculation region. In particular, the unsteady movement of the reattachment point is highly correlated with the flapping motion, and so is the maximum reverse flow. As a result, the flapping motion contributes substantial parts of the Reynolds shear stress and turbulent kinetic energy within the shear layer in the latter half of the reattachment length.
REFERENCES
1.
J. K.
Eaton
and J. P.
Johnston
, “A review of research on subsonic turbulent-flow reattachment
,” AIAA J.
19
, 1093
–1100
(1981
).2.
G. L.
Brown
and A.
Roshko
, “On density effects and large structure in turbulent mixing layers
,” J. Fluid Mech.
64
(4
), 775
–816
(1974
).3.
C.
Chandrsuda
and P.
Bradshaw
, “Turbulence structure of a reattaching mixing layer
,” J. Fluid Mech.
110
, 171
–194
(1981
).4.
T. R.
Troutt
, B.
Scheelke
, and T. R.
Norman
, “Organized structures in a reattaching separated flow field
,” J. Fluid Mech.
143
, 413
–427
(1984
).5.
F.
Scarano
, C.
Benocci
, and M. L.
Riethmuller
, “Pattern recognition analysis of the turbulent flow past a backward-facing step
,” Phys. Fluids
11
(12
), 3808
–3818
(1999
).6.
P.
Bradshaw
and F. Y. F.
Wong
, “The reattachment and relaxation of a turbulent shear layer
,” J. Fluid Mech.
52
(1
), 113
–135
(1972
).7.
E. W.
Adams
and J. P.
Johnston
, “Flow structure in the near-wall zone of a turbulent separated flow
,” AIAA J.
26
(8
), 932
–939
(1988
).8.
J. K.
Eaton
and J. P.
Johnston
, “Low frequency unsteadyness of a reattaching turbulent shear layer
,” in Turbulent Shear Flow 3
(Springer-Verlag Press
, 1982
).9.
I.
Lee
, S. K.
Ahn
, and H. J.
Sung
, “Three-dimensional coherent structures in a separated and reattaching flow over a backward-facing step
,” Exp. Fluids
36
, 373
–383
(2004
).10.
D. M.
Driver
, H. L.
Seegmiller
, and J.
Marvin
, “Time-dependent behavior of a reattaching shear layer
,” AIAA J.
25
, 914
–919
(1987
).11.
R. L.
Simpson
, “Turbulent boundary-layer separation
,” Annu. Rev. Fluid Mech.
21
, 205
–234
(1989
).12.
M. A. Z.
Hasan
, “The flow over a backward-facing step under controlled perturbation: Laminar separation
,” J. Fluid Mech.
238
, 73
–96
(1992
).13.
F.
Heenan
and J. F.
Morrison
, “Passive control of pressure fluctuations generated by separated flow
,” AIAA J.
36
(6
), 1014
–1022
(1998
).14.
P. G.
Spazzini
, G.
Iuso
, M.
Onorato
, N.
Zurlo
, and G. M.
di Cicca
, “Unsteady behavior of back-facing step flow
,” Exp. Fluids
30
, 551
–561
(2001
).15.
V.
Statnikov
, I.
Bolgar
, S.
Scharnowski
, M.
Meinke
, C. J.
Kähler
, and W.
Schröder
, “Analysis of characteristic wake flow modes on a generic transonic backward-facing step configuration
,” Eur. J. Mech., B: Fluids
59
, 124
–134
(2016
).16.
L. M.
Hudy
and A.
Naguib
, “Stochastic estimation of a separated-flow field using wall-pressure-array measurements
,” Phys. Fluids
19
, 024103
(2007
).17.
P.
Huerre
and P. A.
Monkewitz
, “Absolute and convective instabilities in free shear layers
,” J. Fluid Mech.
159
, 151
–168
(1985
).18.
D.
Wee
, T.
Yi
, A.
Annaswamy
, and A. F.
Ghoniem
, “Self-sustained oscillation and vortex shedding in backward-facing step flow: Simulation and linear instability analysis
,” Phys. Fluids
16
, 3361
–3373
(2004
).19.
F. W.
Roos
and J. T.
Kegelman
, “Control of coherent structures in reattaching laminar and turbulent shear layers
,” AIAA J.
24
(12
), 1956
–1963
(1986
).20.
S.
Bhattacharjee
, B.
Scheelke
, and T. R.
Troutt
, “Modification of vortex interactions in a reattaching separated flow
,” AIAA J.
24
, 623
–629
(1986
).21.
T. M.
Farabee
and M. J.
Casarella
, “Measurements of fluctuating wall pressure for separated/reattached boundary layer flows
,” J. Vib. Acoust. Stress Reliab. Des.
108
, 301
–307
(1986
).22.
Y. Z.
Liu
, W.
Kang
, and H. J.
Sung
, “Assessment of the organization of a turbulent separated and reattaching flow by measuring wall pressure fluctuations
,” Exp. Fluids
38
, 485
–493
(2005
).23.
H.
Wengle
, A.
Huppertz
, G.
Bärwolff
, and G.
Janke
, “The manipulated transitional backward-facing step flow: An experimental and direct numerical simulation investigation
,” Eur. J. Mech., B: Fluids
20
, 25
–46
(2001
).24.
J.
Kostas
, J.
Soria
, and M. S.
Chong
, “Particle image velocimetry measurements of a backward-facing step flow
,” Exp. Fluids
33
, 838
–853
(2002
).25.
P. S.
Zanko
, A.
Pollpard
, and N. I.
Miheev
, “Unsteady phenomena in separated and reattaching flows: From statistical characteristics to instantaneous space-time fields
,” in 15th International Symposium on Flow Visualization
, Belarus
, 2012
.26.
F. F. J.
Schrijer
, A.
Sciacchitano
, and F.
Scarano
, “Spatio-temporal and modal analysis of unsteady fluctuations in a high-subsonic base flow
,” Phys. Fluids
26
, 086101
(2014
).27.
R.
Sampath
and S. R.
Chakravarthy
, “Proper orthogonal and dynamic mode decompositions of time-resolved PIV of confined backward-facing step flow
,” Exp. Fluids
55
, 1792
(2014
).28.
X.
Ma
, R.
Geisler
, J.
Agocs
, and A.
Schröder
, “Investigation of coherent structures generated by acoustic tube in turbulent flow separation control
,” Exp. Fluids
56
, 46
(2015
).29.
X.
Ma
, R.
Geisler
, and A.
Schröder
, “Experimental investigation of three-dimensional vortex structures downstream of vortex generators over a backward-facing step
,” Flow, Turbul. Combust.
98
, 389
–415
(2016
).30.
S.
Scharnowski
, I.
Bolgar
, and C. J.
Kähler
, “Characterization of turbulent structures in a transonic backward-facing step flow
,” Flow, Turbul. Combust.
98
(4
), 947
–967
(2016
).31.
V. W.
Goldschmidt
and P.
Bradshaw
, “Flapping of a plane jet
,” Phys. Fluids
16
(3
), 354
–355
(1973
).32.
F.
Durst
and C.
Tropea
, “Flows over two-dimensional backward-facing steps
,” in IUTAM Symposium, Marseille, France
, edited by R.
Dumas
and L.
Fulachier
(Springer International Publishing AG
, 1982
), pp. 41
–52
.33.
P. M.
Nadge
and R. N.
Govardhan
, “High Reynolds number flow over a backward-facing step: Structure of the mean separation bubble
,” Exp. Fluids
55
, 1657
(2014
).34.
D.
Rockwell
and C.
Knisely
, “Vortex-edge interaction: Mechanisms for generating low frequency components
,” Phys. Fluids
23
(2
), 239
–240
(1980
).35.
C.
Knisely
and D.
Rockwell
, “Self-sustained low-frequency components in an impinging shear layer
,” J. Fluid Mech.
116
, 157
–186
(1982
).36.
V.
de Brederode
and P.
Bradshaw
, “Influence of the side walls on the turbulent center-plane boundary layer in a square duct
,” J. Fluids Eng.
100
, 91
–96
(1978
).37.
C. J.
Kähler
, B.
Sammler
, and J.
Kompenhans
, “Generation and control of tracer particles for optical flow investigations in air
,” Exp. Fluids
33
, 736
–742
(2002
).38.
M.
Raffel
, C. E.
Willert
, S. T.
Wereley
, and J.
Kompenhans
, Particle Image Velocimetry: A Practical Guide
(Springer-Verlag Press
, 2007
).39.
C. E.
Willert
and M.
Gharib
, “Digital particle image velocimetry
,” Exp. Fluids
10
, 181
–193
(1991
).40.
L.
Lumley
, “The structure of inhomogeneous turbulent flow
,” in Atmospheric Turbulence and Radio Wave Propagation
, edited by A. M.
Yaglom
and V. I.
Tatarsky
(Defense Technical Information Center
, Moscow
, 1967
), pp. 166
–178
.41.
L.
Sirovich
, “Turbulence and the dynamics of coherent structures. Part 1: Coherent structures
,” Q. Appl. Math.
45
(3
), 561
–571
(1987
).42.
E.
Meyer
, J. M.
Pedersen
, and O.
Özcan
, “A turbulent jet in crossflow analysed with proper orthogonal decomposition
,” J. Fluid Mech.
583
, 199
–227
(2007
).43.
B. P.
Epps
and H. A.
Techet
, “An error threshold criterion for singular value decomposition modes extracted from PIV data
,” Exp. Fluids
48
, 355
–367
(2010
).44.
L. H.
Benedict
and R. D.
Gould
, “Towards better uncertainty estimates for turbulence statistics
,” Exp. Fluids
22
, 129
–136
(1996
).45.
B. F.
Armaly
, F.
Durst
, J. C. F.
Pereira
, and B.
Schönung
, “Experimental and theoretical investigation of backward-facing step flow
,” J. Fluid Mech.
127
, 473
–496
(1983
).46.
C. M.
Ho
and P.
Huerre
, “Perturbed free shear layers
,” Annu. Rev. Fluid Mech.
16
, 365
–424
(1984
).47.
R.
Perrin
, M.
Braza
, E.
Cid
, S.
Cazin
, A.
Barthet
, A.
Sevrain
, C.
Mockett
, and F.
Thiele
, “Obtain phase averaged turbulence properties in the near wake of a circular cylinder at high Reynolds number using POD
,” Exp. Fluids
43
, 341
–355
(2007
).© 2017 Author(s).
2017
Author(s)
You do not currently have access to this content.
